Method and apparatus for acoustical power transfer and communication using steel wedges

ABSTRACT

Systems and methods for transmitting power and information using acoustic energy produced by transducers are provided. The systems have particular application for powering and communication with electronics through drilling and pipe systems. Pairs of acoustic wedges holding transducers are provided for sending energy and information through a substrate which may be a steel pipe. Each wedge has an angled transducer which can be used to produce shear waves. The waves propagate through the substrate and are received by a second acoustic wedge. The shear waves, on reaching the second acoustic wedge, are converted back into electrical signals by a second transducer. Tangential shear waves, high, shallow wave transmission angles, and direct steel-steel bonding between wedges and substrates may be used.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation of U.S. patent application Ser. No.15/119,302, filed Aug. 16, 2016, which is a national stage filing ofInternational Patent Application No. PCT/US2015/017268, filed Feb. 24,2015, which claims the benefit of U.S. Provisional Application Ser. No.61/944,916, filed Feb. 26, 2014, which is incorporated herein byreference in its entirety.

FIELD AND BACKGROUND OF THE INVENTION

The present invention relates generally to the field of acoustics, andin particular to transducers, to communication and power transmissionusing vibrations, and to taking sensor readings in deep wells.

A transducer is a device that converts a signal in one form of energy toanother form of energy. This can include electrical energy, mechanicalenergy, electromagnetic and light energy, chemical energy, acousticenergy, and thermal energy, among others. While the term “transducer”often refers to a sensor or a detector, any device which converts energycan be considered a transducer.

Transducers are often used in measuring instruments. A sensor is used todetect a parameter in one form and report it in another form of energy,typically as an electrical signal. For example, a pressure sensor mightdetect pressure—a mechanical form of energy—and convert it toelectricity for display for transmission, recording, and/or as a powersource. A vibration powered generator is a type of transducer thatconverts kinetic energy derived from ambient vibration to electricalenergy.

A transducer can also be an actuator which accepts energy and producesmovement, such as vibrational energy or acoustic energy. The energysupplied to an actuator might be electrical or mechanical, such aspneumatic or hydraulic energy. An electric motor and a loudspeaker areboth actuators, converting electrical energy into motion for differentpurposes.

Some transducers have multiple functions, both detecting and creatingaction. For example, an ultrasonic transducer may switch back and forthmany times a second between acting as an actuator to produce ultrasonicwaves, and acting as a sensor to detect ultrasonic waves and convertingthem into electrical signals. Analogously, rotating a DC electricmotor's rotor will produce electricity, and voice-coil speakers can alsofunction as microphones.

Piezoelectric materials can be used as transducers to harvest even lowlevels of mechanical energy and convert them into electrical energy.This energy can be suitable for powering wireless sensors, low powermicroprocessors, or charging batteries. A piezoelectric sensor ortransducer is a device that uses a piezoelectric effect to measurepressure, acceleration, strain, or force by converting those physicalenergies into an electrical charge. The piezoelectric effect is areversible process in that materials exhibiting the direct piezoelectriceffect (generation of an electrical charge as a result of an appliedmechanical force) also exhibit the reverse piezoelectric effect(generating a mechanical movement when exposed to an electrical chargeor field). Thus, piezoelectric transducers can also work in reverse,turning electrical energy into physical vibrational energy and viceversa. Piezoelectric transducers have the dual advantages of workingusing low energy levels, and a small physical size. Ultrasonictransducers may be piezoelectric transducers, applying ultrasound wavesinto a body, and also receiving a returned wave from the body andconverting it into an electrical signal.

In drilling and oil well operations, it is often necessary tocommunicate information (such as sensor data) along a drill pipe string.A drill pipe string consists of connected segments of piping. Often,portions of the well and drill string are not directly accessible via adirect electrical connection. For example, there may be segments thatare disjointed and sealed off from each other, making electricalconnection between the segments impossible. Since it is desirable toobtain data from deep within wells, passage of the data through theseobstacles is a significant issue.

Accordingly, one method and arrangement for powering, controlling, andcommunicating with sensors at a distance uses acoustic wave energy. Thearrangement comprises a transmission arrangement comprising an acousticsignal generator, a receiving arraignment comprising an acoustic signalreceiver, a least one sensor which is electrically coupled to the signalreceiver, and a waveguide spanning between and engaged to the signalgenerator and the signal receiver. An acoustical wave preferablycomprising a control signal can be generated with the signal generator,the acoustical wave preferably having sufficient strength to provideoperating power to the sensor. The acoustical wave is transmitted fromthe signal generator to the signal receiver through the waveguide. Theacoustical wave is received at the signal receiver, and converted intoan electrical current optionally comprising a converted control signal.Preferably the electrical current is also used to power a sensor,communication device and/or other devices in the vicinity of thereceiving arrangement. A control signal can simultaneously oralternatively be transmitted by the above method, such as by modulatingthe acoustic wave.

Transmitting and receiving arrangements can comprise piezoelectrictransducers, where the signal generator piezoelectric transducergenerates an acoustical wave comprising a control signal in response toelectrical current applied to it. The signal receiver piezoelectrictransducer then receives at least part of the acoustical wave, andconverts at least a portion of the received acoustical wave into anelectrical current which is then used to power and/or control thesensor. The sensor is not limited to any one sensor, and may detectpressure, temperature, vibrations, sounds, light, or other conditions.

It is possible to power one or more sensors exclusively usingelectricity generated by the signal receiver piezoelectric transducer,particularly sensors with low power requirements.

In one useful configuration, the transmission arrangement is aboveground, while the receiving arraignment and a sensor are below ground,such as in a mine, well, tunnel, or shaft. Waves transmitted from thesignal generator to the signal receiver through the waveguide can beused to power and control the sensor below ground. Waves in the reversedirection can transmit sensor data or other data back to the sametransmission arrangement, or to a different arrangement provided forthat purpose.

Waves can be modulated in a variety of known ways to create the controlsignal. In a preferred embodiment a continuous wave for transmittingpower is selectively modulated when it is desired to send signals orinformation in addition to or instead of operating power.

A method of transmitting at least one of power and signals along asubstrate using angle beam probes can include: providing a transmittingacoustic wedge and a receiving acoustic wedge spaced apart on asubstrate and coupled to the substrate at respective interfaces; whereineach acoustic wedge comprises a transition wedge and a transducercomprising a transducer face, wherein the transducer is coupled to thetransition wedge, and wherein a transducer face of each transducer isnormal to an angle .theta. with regard to the substrate at therespective interface; wherein, in some arrangements: the transducer faceof the transmitting transducer of the transmitting acoustic wedge isnormal to an angle Θ₁ with respect to the respective interface with thesubstrate, the angle Θ₁ in some embodiments between first and secondcritical angles such that longitudinal waves produced by thetransmitting transducer are substantially converted into shear waves inthe substrate; in some arrangements the method further comprisingproducing longitudinal waves at angle Θ₁ at the transmitting transducer;in some arrangements, the longitudinal waves producing substantiallyonly shear waves in the substrate, and the shear waves propagatingthrough the substrate until reaching the interface between the substrateand the receiving acoustic wedge; in some arrangements, energy from theshear waves providing acoustical wave energy which reaches the receivingtransducer of the receiving acoustic wedge; and the receiving transducerconverting at least a portion of said acoustical wave energy intoelectrical energy.

In alternative arrangements, shear waves created by angled longitudinalwaves can be used to send power and/or signals down the length of asubstrate such as a steel pipe in an oil well.

A transmitting acoustic wedge and a receiving acoustic wedge can beprovided spaced apart on a substrate and coupled to the substrate atrespective interfaces. In one embodiment each acoustic wedge comprises atransition wedge and a transducer comprising a transducer face. Thetransducer is coupled to the transition wedge, and a transducer face ofeach transducer is normal to an angle .theta. with regard to thesubstrate at the respective interface. A preferably planar transducerface of the transmitting transducer of the transmitting acoustic wedgeis normal to an angle Θ₁ with respect to the respective interface withthe substrate, the angle Θ₁ being between first and second criticalangles such that longitudinal waves produced by the transmittingtransducer are substantially converted into shear waves in thesubstrate.

One method further includes producing longitudinal waves at angle.theta..sub.1 at the transmitting transducer. The longitudinal wavesproduce only or substantially only shear waves in the substrate, and theshear waves propagate through the substrate until reaching the interfacebetween the substrate and the receiving acoustic wedge. Energy from theshear waves provides acoustical wave energy which reaches the receivingtransducer of the receiving acoustic wedge, and the receiving transducerconverts at least a portion of said acoustical wave energy intoelectrical energy. The energy can be used to transmit power and/orsignals to sensors or other electronics. This is particularly useful forsensors and electronics deep underground.

In some arrangements, most or all of the shear wave energy which reachesthe receiving acoustic wedge converts back to longitudinal waves at thereceiving acoustic wedge. The receiving transducer of the receivingacoustic wedge then receives at least a portion of the longitudinalwaves and converts at least a portion of said longitudinal waves intoelectrical energy.

In previously known arrangements, the substrate comprises metal(s) suchas steel, and the transition wedges are acrylic. The substrate may be ametal pipe, such as in an oil well.

In some arrangements, wedge, transducer, and substrate methods andapparatus can also be used to send signals in the reverse direction fromthe receiving acoustic wedge to the transmitting acoustic wedge. Thestep of sending signals in the reverse direction comprises the receivingtransducer generating waves at an angle with respect to the respectiveinterface with the substrate, the angle being between first and secondcritical angles, and the waves propagating through the substrate to thereceiving acoustic wedge.

In another arrangement, the transition wedge of the transmittingacoustic wedge includes a generally slanted edge which is normal to anangle .theta..sub.1 with respect to the respective interface with thesubstrate. Typically a flat or planer face of a transducer is fixed tothe slanted edge so that the transducer face is oriented in the samedirection, i.e. on the same plane, as the slanted edge. In practice, theorientation of the transducer will often be selected by selecting aproper angle for the slanted edge. Thus, preferably, the slanted edge isnormal to an angle .theta..sub.1 is between first and second criticalangles such that longitudinal waves produced by the transmittingtransducer are substantially converted into shear waves in thesubstrate.

Though the substrate may be a large item with a large surface area andvaried shape, the angle of the substrate where the respective acousticwedges and transducers are located is a key angle of concern inselecting longitudinal wave angles. Typically this will be the angle atan interface between each acoustic wedge and the substrate.

Proper angles for launching longitudinal waves to produce shear waves ina substrate can be determined using Snell's law. The angle Θ₁ betweenfirst and second critical angles can be the longitudinal wave launchangle Θ_(1Longitudinal). Thus, the method of the invention can includethe step of determining Θ_(1Longitudinal) using the relationship:

${\arcsin \left( \frac{V_{1{Longitudinal}}}{V_{2{Longitudinal}}} \right)} < \theta_{1{Longitudinal}} < {\arcsin \left( \frac{V_{1{Longitudinal}}}{V_{2{Shear}}} \right)}$

wherein V_(1Longitudinal) is the longitudinal wave speed in thetransition wedge, V_(2Longitudinal) is the longitudinal wave speed inthe substrate, and V_(2Shear) is the shear wave speed of the substrate.This is a method for determining the angle and orientation of thetransducers and/or slanted edges supporting the transducers.

Longitudinal wave are waves where the displacement of the medium is inthe same direction as, or the opposite direction to, the direction oftravel of the wave. Mechanical longitudinal waves are also calledcompression waves, because they produce compression and rarefaction whentraveling through a medium.

A shear or transverse wave is a moving wave that consists ofoscillations occurring perpendicular (i.e. at right angles) to thedirection of energy transfer. If a shear wave is moving in the positivex-direction, its oscillations are in up and down in the y-z plane. Withtransverse waves in matter, the displacement of the medium isperpendicular to the direction of propagation of the wave. A ripple in apond or a wave on a string are examples of transverse waves.

Power and Communication Transmission Through a Surface Via Angled Waves

For digital acoustic communication and acoustic power transfer along asubstrate, continuous acoustic waves are transmitted along the substratechannel between a pair of electromechanical transducers. This technologyallows remote sensing of sealed environments. A better understanding ofwave propagation will allow for systems that will operate moreefficiently and can act over larger ranges. Although guided wave modesin the substrate have been more extensively studied than bulk waves,wedge-introduced bulk waves have shown the potential to outperform themin some situations. Advantages include directionality of the wave fieldand simplicity of implementation; to excite guided modes, it is in manycases necessary to use numerous transducers, while when using wedgeintroduced bulk waves, a pair will often be sufficient, especially overshort range.

As mentioned, in drilling and oil well operations, it is often necessaryto communicate information (such as sensor data) along a drill pipestring where portions of the well and drill string are not directlyaccessible via a direct electrical connection. For example, there may besegments that are disjointed and sealed off from each other, makingelectrical connection between the segments impossible. An alternativeaspect of the present invention is therefore an improved means ofpassing both power and data through drill pipe strings, includingstrings having blocked off sections, using acoustic waves sent throughthe pipe itself.

The system can simultaneously transmit both digital information and/orpower, preferably in both directions, through the wall of a pipe orother analogous substrate using ultrasound from an angle beam probe. Theangle beam probe may comprise transducers, such as an ultrasonicpiezoelectric transducers.

Similar power communication systems can be implemented usinglongitudinal waves by using magnetostrictive means as well.Magnetostrictive materials can convert magnetic energy into kineticenergy, and vice versa.

One transmission system, shown schematically in FIG. 1, consists of twoacoustic wedges 40,50, which may be sending and receiving acousticwedges. Each acoustic wedge preferably includes a transition wedge 44,54and a transducer 41,51. Each transducer preferably includes a generallyplanar face 47,57. Each transition wedge preferably has at least oneslanted edge 46,56. The planar face of a transducer may be fixed to aslanted edge to fix and orient the planar face at a given angle. Theangle of the slanted edge, or other aspects of the shape of thetransition wedges, may be selected in order to support a transducer at aselected angle. A transition wedge may, in some embodiments, resemble arectangular solid with a corner sliced off to provide the slanted edge,although the invention is not limited to any particular shape. Typicallya bottom side of each transition wedge 44,54 is engaged to the substrate60. The interface 48,58 of the substrate and the wedges should be asseamless as possible for sending and receiving wave energy. A signalsender/receiver, typically a transducer 41,51, is fixed to a slantededge on the transition wedge so that a flat face of the transducer is atan intermediate angle with regard to the plane of the substrate 75 atthe interface 48,58. The acoustic wedges may also be triangles or othershapes. Various arrangements to provide transducers at an angle withregard to the substrate are within the scope and spirit of theinvention. In one embodiment a surface transducer A 41 is located aboveground, and a second transducer B 51 is located underground.

The first acoustic wedge 40 sends longitudinal waves 70 launched bytransmitting transducer a 41 through a transition block or wedge 44 intoa plate or cylindrical shell 60 (e.g., pipe) at an angle such that onlytransverse (shear) waves 75 are produced in the plate/shell 60. Thelaunch angle in the wedge 40,50 is selected such that it is between thefirst and second critical angles, so that substantially only shear waveswill be produced in the wall 60. These shear waves 75 propagate down thewall 60 to a second acoustic wedge 50 which is angled such that thereceived shear waves 75 are converted back into longitudinal waves 70within the transition wedge 54. The longitudinal waves 70 are thencaptured by the second receiving acoustic transducer B 51. In allembodiments, sending and receiving transducers may be the same ordifferent. In one embodiment above-ground sending 41 and below-groundreceiving 51 transducers are essentially the same other than theirpositions in the system. In some embodiments both sending and receivingtransducers send and receive acoustic wave signals.

A portion of the acoustic energy captured by the receiving transducer B51 can be harvested to produce electric energy in order to power sensors90 or other devices 90 located in the same region as the second acousticwedge 50 and transducer B 51. Referring to FIG. 1, the data generated bythe sensors 90 near “receiving” transducer B may be sent back to thefirst “sending” transducer A 41. The data may be sent back digitallyfrom transducer B 51 along a wall 60 to transducer A 41, where the datamay be properly stored, displayed, or retransmitted. Data from thevicinity of transducer B 51 may also be sent elsewhere, and by otherknown methods. Data may also be sent back using shear waves using themethod above in the reverse direction.

FIG. 2 is a background illustration and equation to help explain theconcept of critical angles.

The critical angle is the angle of incidence above which total internalreflection occurs. The angle of incidence is typically measured withrespect to the normal at the refractive boundary. Total internalreflection occurs when a propagating wave strikes a medium boundary atan angle larger than a particular critical angle with respect to thenormal to the surface. If the refractive index is lower on the otherside of the boundary and the incident angle is greater than the criticalangle, the wave cannot pass through and is entirely reflected. This isparticularly common as an optical phenomenon, where light waves areinvolved, but it occurs with other types of waves, such aselectromagnetic waves in or sound waves.

When a wave crosses a boundary between materials with differentrefractive indices, the wave will be partially refracted at the boundarysurface, and partially reflected. However, if the angle of incidence isgreater than the critical angle—if the direction of propagation or rayis closer to being parallel to the boundary—then the wave will not crossthe boundary and instead be totally reflected back internally. This canonly occur where the wave travels from a medium with a higher refractiveindex to one with a lower refractive index. For example, it will occurwith light when passing from glass to air, but not when passing from airto glass.

Consider a light ray passing from glass into air or. The light emanatingfrom the interface is bent towards the glass. When the incident angle isincreased sufficiently, the transmitted angle (in air) reaches 90degrees. It is at this point no light is transmitted into air. Thecritical angle Θ_(1Critical) is given by Snell's law. FIG. 2 Illustratesan analogous relationship with a ray of light passing from water intoair.

FIG. 3 shows the relationship between the incident angle of the angularlongitudinal wave and the relative amplitudes of the refracted and/ormode converted longitudinal, shear, and surface waves that can beproduced in the substrate. The method of the invention makes use of thestrong shear waves which can be created by using the proper incidentangle between the first and second critical angles.

Using Snell's law, the refraction angles (e.g. angles Θ₁ and Θ₂ inFIG. 1) for use in applicable embodiments may be determined from:

$\frac{\sin \; \theta_{1{Longitudinal}}}{V_{1{Longitudinal}}} = {\frac{\sin \; \theta_{2{Shear}}}{V_{2{Shear}}} = {\frac{\sin \; \theta_{2{Longitudinal}}}{V_{2{Longitudinal}}} = \frac{\sin \; \theta_{1{Shear}}}{V_{1{Shear}}}}}$

To produce only a shear wave in the plate/shell/pipe 60, thelongitudinal launch angle Θ_(1Longitudinal) has to be between the firstand second critical angles, which will be produced as long as thelongitudinal wave in the launch material has a sound speed less than theshear wave speed of the steel:

${\arcsin \left( \frac{V_{1{Longitudinal}}}{V_{2{Longitudinal}}} \right)} < \theta_{1{Longitudinal}} < {\arcsin \left( \frac{V_{1{Longitudinal}}}{V_{2{Shear}}} \right)}$

For example, one available launch material in is acrylic (which may bePerspex), which has a longitudinal wave speed ofV_(1Longitudinal acrylic)=2,730 m/s. The first critical launch angle isfound by setting Θ_(2Longitudinal) to 90°, giving the first criticalangle:

${\sin \mspace{14mu} \theta_{1\mspace{11mu} {Longitudinal}\mspace{11mu} {First}\mspace{11mu} {Critical}}} = \frac{V_{1{Longitudinal}}}{V_{2{Longitudinal}}}$

and the second critical launch angle is found by setting Θ_(2Shear) to90°, giving the second critical angle

${\sin \mspace{14mu} \theta_{1\mspace{11mu} {Longitudinal}\mspace{14mu} {Second}\mspace{14mu} {Critical}}} = \frac{V_{1{Longitudinal}}}{V_{2{Shear}}}$

If, for example, the wall used with the above acrylic launch wedge ismade of steel with a shear wave speed of V_(2Shear)=3,250 m/s, and alongitudinal wave speed of V_(2Longitudinal)=6,100 m/s, then theseangles are:

$\theta_{1\mspace{11mu} {Longitudinal}\mspace{11mu} {First}\mspace{11mu} {Critical}} = {{\arcsin \left( \frac{V_{1{Longitudinal}}}{V_{2{Longitudinal}}} \right)} = {{\arcsin \left( {2.730/6100} \right)} = {26.57{^\circ}}}}$$\theta_{1\mspace{11mu} {Longitudinal}\mspace{14mu} {Second}\mspace{14mu} {Critical}} = {{\arcsin \left( \frac{V_{1{Longitudinal}}}{V_{2{Shear}}} \right)} = {{\arcsin \left( {2.730/3250} \right)} = {57.11{^\circ}}}}$

Another material that can be used for higher temperature applications isTeflon, with a longitudinal wave speed of 1,372 m/s, and correspondingfirst and second critical angles of 13.46 degrees and 24.96 degrees,respectively.

So, forΘ_(1Longitudinal First Critical)<Θ₁<Θ_(1Longitudinal Second Critical),only shear waves at an angle Θ_(2Shear) will be present in thecommunications channel. In addition, this system can also be adjusted bylaunching pure shear waves at angle Θ_(1Shear) using a shear wavetransducer in addition to or instead of the above arrangement startingwith angled longitudinal waves. Note that there will also be two wavesgenerated in at least the transmitting wedge 44,54, due to reflection,Θ_(1Longitudinal) and Θ_(1Shear). These reflected waves are eitherscattered or absorbed by the other wall of the wedge.

Many different channel modulation techniques are suitable for thesearrangements. Non-limiting examples include traditional single-carriermodulations such as amplitude modulation (AM), frequency modulation(FM), ON-OFF Keying (OOK), amplitude-shift keying (ASK), phase-shiftkeying (PSK), differential phase-shift keying (DPSK), frequency-shiftkeying (FSK) and quadrature amplitude modulation (QAM).

Multi-carrier modulations such as orthogonal frequency-divisionmultiplexing can also be used and will, in general, provide higher datarates for the channel. Multi-carrier techniques offer the ability tooptimize the transmission for the specific transfer function that thechannel presents though the use of bit loading. In bit loading eachsubcarrier uses a modulation type that provides the highest data rategiven the signal-to-noise ratio (SNR) of that particular subcarrierchannel. Multi-carrier techniques can instead or in addition includepower loading, in which the transmit power of each subcarrier is alsoadjusted to optimize the data throughput over all subcarriers given anoverall power budget.

FIG. 4 shows a side view of an exemplary acoustic wedge mounted on a ⅞″diameter, 0.7 inch thick steel pipe substrate. The arrangement includesa transition wedge and a mounted transducer. FIG. 5 shows a section ofthe same pipe with a pair of acoustic wedges mounted thereon for usewith the invention.

FIGS. 6 and 7 are computer generated images showing shear wavepropagation. The shear waves are launched via a longitudinal wave sentthrough an acrylic wedge into a 0.7 inch (17.78 mm) thick submergedsteel plate substrate. In both figures the Wedge is the triangle at topleft, and the steel plate substrate is the thick horizontal line at thecenter with water above and below it. FIG. 6 shows the (pressure) 0.3 inthe beam and wedge. FIG. 7 shows the xy deviatoric stress (the log ofthe Von Mises stress) in the beam and wedge. Both figures show the(pressure) 0.3 in the water.

FIGS. 8-10 are plots of the log of the amplitude of the pressure in thesteel substrate and acrylic wedge at three different frequencies: 0.5(FIG. 8), 1.0 (FIG. 9), and 2.25 (FIG. 10) MHz. It makes the standingwave in the solids more clear. Also the beam is now 8″ instead of 3″.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide novel improvedmethods and arrangements for transmitting power and signals usingacoustical waves and energy. Preferred methods and arrangements transmitpower and information using shear waves, preferably tangentiallypolarized shear waves, through a substrate such as a pipe. Preferredmethods also utilize transmission wedges made of the same material (suchas steel) as the substrate, and which have a high transducer launchangle.

The systems have particular application for powering and communicationwith electronics such as sensors in oil or gas wells using acousticenergy where powering and communication via electric wires is notpossible. For example, the system may be configured to employ acousticenergy to power and communicate with a sensor/transmitter disposed onthe high pressure side of a packer where the packer provides a sealbetween the outside of the production tubing and the inside of thecasing or well bore wall. Packer is a type of seal at the end of aproduction pipe. It has historically been extremely difficult toposition and use electronics below the packer, and the instant inventionaddressees that problem.

Typical embodiments of the system include a transmission arrangementcomprising an acoustic signal generator, a receiving arrangementcomprising an acoustic signal receiver, at least one sensor which iselectrically coupled to the signal receiver, and a waveguide orsubstrate (e.g., casing or wellbore wall) spanning between the signalgenerator and the signal receiver/sensor. Specifically, the arrangementmay include a transmitting acoustic wedge and a receiving acoustic wedgespaced apart on the waveguide or substrate. The instant inventionincludes improvements to optimize the transfer of acoustic energy and toimprove efficiency of the system. For example, such aspects may includethe following:

Using tangentially polarized shear acoustic waves, particularly when oneor more surfaces of the substrate (often the wall of a metal pipe)contact liquid such as oil or water. Tangential shear waves vibrate sideto side “within” the metal substrate, and therefore have minimalinteraction with the liquid. Radial shear waves, in contrast, vibrate inand out of the plane of the metal substrate and therefore push upagainst liquid contacting the substrate. The liquid, in turn, absorbsenergy from the radial shear waves which dissipates the transmission.

Preferred wedges are made of the same material as the substrate. Forexample, steel may be used for both the wedge and substrate, such as asteel pipe. Waves produced in the steel wedge at an angled launchsurface will continue into a substrate made of the same material largelyunaffected. Such configurations are believed to reduce the acousticpower reflection coefficient at the interface between the wedge and thesubstrate. This improves efficiency.

The acoustic transmitter and acoustic receiver are preferably eachattached to an angled surface of a wedge. Preferred angled surfaces areelevated between about 65 or 70 degrees and about 80 or 85 degrees withrespect to the substrate below. Adjustment of the launch angle may leadto higher energy transfer efficiency.

Placing the wedges on portions of the substrate which will receivestrong vibrational transmissions from the other wedge and, as acorollary, avoiding placing wedges in “dead zones” along the substrate.The location of dead zones is often periodic, and will vary depending onthe transmission angles, frequencies, properties of the substrate, andother factors.

Using two adjacent transmitting wedges may make the receiving substratedisplacement field more uniform and avoid dead zones.

The direction of power transmission is generally defined as the“forward” direction. Forward power transmission, and data transmissionin the opposite (reverse) direction, can be accomplished by using acombined system. Forward data transmission, in the same direction as thepower transmission, can also be implemented, such as by modulating thepower signal.

The improved system can simultaneously transmit both digital informationand/or power, preferably in both directions, through the wall of a pipeor other analogous substrate using ultrasound from an angle beam probe.The angle beam probe may comprise transducers, such as an ultrasonicpiezoelectric transducers.

A preferred system comprises two acoustic wedges, which may be sendingand receiving acoustic wedges. Each acoustic wedge preferably includes atransition wedge and a transducer fixed to the wedge. Each transducerpreferably includes a generally planar face. Each transition wedgepreferably has at least one slanted edge. The planar face of atransducer is typically fixed to a slanted edge of the wedge to fix andorient the planar face of the transducer at a given angle. The angle ofthe slanted edge, or other aspects of the shape of the transitionwedges, may be selected in order to support a transducer at a selectedangle. A transition wedge may resemble a rectangular solid with a cornersliced off to provide the slanted edge, or may be a triangular solidresembling half of a rectangular solid which has been diagonally cut inhalf from one edge to a diagonally opposite edge, although the inventionis not limited to any particular shape. Various arrangements to providetransducers at an angle with regard to the substrate are within thescope and spirit of the invention. Typically a bottom side of eachtransition wedge is engaged to the substrate, in some embodiments beingfully fused to the substrate or being an integral component of thesubstrate. In preferred embodiments the transition wedges(s) are made ofthe same material as the substrate. The interface of the substrate andthe wedges should be as seamless as possible for sending and receivingwave energy.

In one embodiment a surface transducer is located above ground, and asecond transducer is located underground.

Current acoustic technologies rely on acrylic wedges as an intermediatebetween the transducers and the substrate to generate shear waves in thesubstrate caused by interfacial diffraction. The large difference inacoustic impedance between the wedge and the substrate (most oftensteel) results in large reflection coefficients, hence reduced detectionsensitivity. We have found that using a wedge made of the same materialas the substrate decreases reflection at the wedge-substrate interface.This invention provides improvements over acoustical communication andpower transfer systems previously developed by the same inventors. Forexample, when the transmitting and/or receiving wedges are made of thesame material as the substrate, then waves produced in the wedge at theangled launch surface will continue into the substrate unaffected.Preferred wedge/substrate materials include steel/steel pairings, andother couplings both using an identical metal, alloy, or composite.These waves can be launched from the wedge launch surface as alongitudinal wave so as to remain longitudinal waves upon entering thesubstrate. In some embodiments, mode conversion (such as fromlongitudinal waves to shear waves) can occur at the opposite receivingsurface or wedge.

Similarly, if shear waves are launched from the wedge/launch surface,they can remain as shear waves when they enter a substrate made of thesame material as the wedge. Shear waves can be propagated with thedirection of wave displacement being in the plane formed by thewedge/substrate interfaces (in-planar polarization); or they can bepropagated perpendicular to the plane of the wedge (transversepolarization).

As mentioned above, one less-preferred method for introducing shearwaves into a metal substrate is via a longitudinal transducer mated toan acrylic wedge. The transducer produces longitudinal waves whichtravel through the acrylic wedge, and which become shear waves at thejoint between the acrylic block and the metal substrate. This methodproduces large acoustic power reflections, and consequently losses, atthe interface of the wedge and the substrate due to a large acousticimpedance mismatch. This effect has been demonstrated in a modelingenvironment, and methods for reducing these losses are desirable. It hasnow been shown that a significant improvement in acoustic transferefficiency between a wedge and substrate may be achieved by using ashear-poled transducer coupled to a steel wedge coupled to a steelsubstrate. This improvement is partially attributed to a reduction inthe acoustic power reflection coefficient at the interface between thewedge and the substrate. In modeling of a system with a perfectinterfacial boundary, it was shown that no energy is reflected off thesubstrate joint and back into the wedge at the interface, withsubstantially all of the energy being transmitted into the joint, evenat very shallow angles of incidence. A steel wedge may also be used witha longitudinal transducer to efficiently introduce longitudinal wavesinto a steel substrate. This concept can be generalized to vibrationcarrying materials other than steel, such as other metals and metalalloys.

A preferred method and arrangement for transmitting at least one ofpower and signals along a steel oil pipe using tangential shear waves,include some or all of the following features and/or steps: atransmitting arrangement and a receiving arrangement spaced apartaxially on a steel oil pipe; wherein the transmitting arrangement isabove ground level and wherein the receiving arrangement is below groundlevel; wherein the oil pipe has concrete on at least a portion of anouter surface, and wherein, in an operative state, oil is in contactwith an inner surface of the oil pipe; wherein each transmittingarrangement comprises a steel transmitting wedge and a transmittingtransducer coupled to the transmitting wedge, and wherein each receivingarrangement comprises a steel receiving wedge and a receiving transducercoupled to the receiving wedge; wherein each transmitting wedge and eachreceiving wedge are directly bound to a surface of the oil pipe by adirect steel-steel bond; wherein the transmitting transducer comprises aflat transmitting face for emitting tangential shear waves, thetransmitting face of the transmitting transducer being coupled to anangled face of the transmitting wedge; wherein the transmitting face ofthe transmitting transducer and the angled face of the transmittingwedge are both normal to an angle .theta. with respect to the surface ofthe oil pipe which the transmitting wedge is coupled to; wherein theangle .theta. is an angle of at least 75 degrees and not more than 85degrees; the method further comprising the transmit transducer producingtangential shear waves launched at angle .theta., with said shear wavespropagating through the transmitting wedge and into the oil pipe,through the oil pipe, and then into the receiving wedge, with saidtangential shear waves being received by the receiving transducer;wherein said tangential shear waves substantially remain tangentialshear waves as they propagate through the transmit wedge, the oil pipe,and the receiving wedge; the receiving transducer converting at least aportion of an energy content of said tangential shear waves intoelectrical energy, and using the electrical energy generated by thereceiving transducer to at least one of provide a control signal andprovide operating electricity for an electronic component.

Alternatively, the angle Θ is an angle of at least 65 or at least 70degrees and not more than 83 degrees, or other angles and rangesdiscussed below. Alternatively, the waves may be longitudinal waves andthe transducers longitudinal wave transducers.

Another preferred method and arrangement for transmitting at least oneof power and signals along a substrate using shear waves includes someor all of the following steps and elements: a transmitting arrangementand a receiving arrangement spaced apart on a substrate; wherein eachtransmitting arrangement comprises a transmitting wedge and atransmitting transducer coupled to the transmitting wedge, and whereineach receiving arrangement comprises a receiving wedge and a receivingtransducer coupled to the receiving wedge; wherein the transmittingtransducer comprises a flat transmitting face for emitting shear waves,the transmitting face of the transmitting transducer being coupled to anangled face of the transmitting wedge; wherein the transmitting face ofthe transmitting transducer is normal to an angle .theta. with respectto the surface of the steel substrate which the transmitting wedge iscoupled to; wherein the angle .theta. is an angle of at least 65 degreesand not more than 89 degrees, at least 70 degrees and not more than 85degrees, or other preferred angles and ranges discussed below; themethod further comprising the transmit transducer producing shear wavesat angle .theta., with said shear waves propagating through thetransmitting wedge and into the substrate, through the substrate, andthen into the receiving wedge, with said shear waves being received bythe receiving transducer; wherein said shear waves substantially remainshear waves as they pass through the transmit wedge, the substrate, andthe receiving wedge; the receiving transducer converting at least aportion of an energy content of said shear waves into electrical energy,and using the electrical energy generated by the receiving transducer toat least one of provide a control signal and provide operatingelectricity for an electronic component.

Alternatively, the waves may be longitudinal waves and the transducerslongitudinal wave transducers.

The arrangement may comprise a plurality of transmitting arrangements,such as 2 or 3 transmitting arrangements, with said transmittingarrangements positioned in series along an axial length of the pipe,wherein said transmitting arrangements all produce shear waves.

The substrate, the transmitting wedge, and the receiving wedgepreferably all comprise steel, and each transmitting wedge and eachreceiving wedge may be directly bound to a surface of the substrate by adirect steel-steel bond.

In other preferred embodiments the substrate, the transmitting wedge,and the receiving wedge are all made of the same material. For example,the same metal or metal alloy. The substrate may be a pipe.

In some arrangements the transmitting arrangement is above ground level,and the receiving arrangement is below ground level. The substrate maybe an oil pipe, wherein the oil pipe has concrete on at least a portionof an outer surface, and wherein, in an operative state, oil is incontact with an inner surface of the oil pipe. Preferably the wedges andsubstrate are all steel.

Transmissions may also sent in a reverse direction, from the receivingacoustic wedge to the transmitting acoustic wedge, using shear wavesproduced by the receiving transducer.

“Poling” refers to the particle displacement direction of the generatedacoustic wave.

The embodiments which follow are presented for the purposes ofillustration only and are not meant to limit the scope of the presentinvention. Most or all of the features of the embodiments in thisdisclosure are interchangeable so that each element in each embodimentmay be applied to all of the embodiments taught herein.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings:

FIG. 1 is a schematic diagram of two acoustic wedges arranged on a pipesubstrate for transmitting wave energy for powering sensors;

FIG. 2 is a diagram showing reflection and refraction of waves reachinga water to air interface at various angles;

FIG. 3 is a graph and diagrams showing the relationship between theincident angle of a wave, and the type of waves produced, when suchwaves in an acrylic wedge reach a steel substrate;

FIG. 4 is a top, side, perspective, closeup view of an acoustic wedgecomprising a transducer mounted on a pipe substrate;

FIG. 5 is a top front perspective view of two acoustic wedges comprisingtransducers mounted along a steel pipe substrate;

FIG. 6 shows pressure in a beam and wedge during shear wave propagation;

FIG. 7 shows stress in a beam and wedge during shear wave propagation;

FIG. 8 shows pressure in a beam and wedge during shear wave propagationat 0.5 MHz;

FIG. 9 shows pressure in a beam and wedge during shear wave propagationat 1.0 MHz;

FIG. 10 shows pressure in a beam and wedge during shear wave propagationat 2.25 MHz;

FIGS. 11a-11d show steady-state harmonic simulations of longitudinal andshear piezoelectric transducers at low (a and b freq(1)=0.1 MHz) andhigh (c and d freq(1)=1.0 MHz) frequencies attached to 70° wedges.Displacement at time t=0 is plotted. FIG. 11(a) is Longitudinal-poled,100 kHz, FIG. 11(b) is Shear-poled, 100 kHz, FIG. 11(c) isLongitudinal-poled, 1 MHz, and FIG. 11(d) Shear-poled, 1 MHz;

FIG. 12 is a model of tangential shear wave transmission. Displacementin meters is plotted. 75° steel wedges are used on a 12 inch steel platewith oil on the inside (top) and cement on the outside (bottom);

FIG. 13 is an isometric view of a tangential (transversely polarized)shear simulation showing the out-of-plane displacement (75° steelwedges, 1 MHz, 12-inch steel plate, oil on the inside (top), cement onthe outside (bottom));

FIG. 14 is a graph of power transfer efficiency across a 4 ft beam as afunction of frequency, with wedge angles 70°, 75°, and 80° fortransversely polarized waves; data from the same tests are tabulated inTable 1;

FIG. 15 is a graphed simulation with both pitcher and catchertransducers. Displacement raised to the fifth root ⅕ is plotted;

FIG. 16 shows voltage at a harvesting transducer plotted over one periodfor 5 different positions of the catching wedge (86 cm, 88 cm, 90 cm, 92cm, and 94 cm);

FIGS. 17(a)-17(b) compare longitudinal wave simulation methods. FIG.17(a) is a prescribed displacement (PD) input, while FIG. 17(b) is atransducer input for comparison;

FIGS. 18(a)-18(b) compare shear wave simulation methods. FIG. 18(a) is aprescribed displacement (PD) input, while FIG. 18(b) is a transducerinput for comparison;

FIG. 19 is a graph of energy flux efficiency in a beam, under dry andsubmerged conditions, at a distance of 8 inches from the transducer;

FIG. 20 is a graph of energy transmission in a simulated beam where theouter wall is bounded by cement and the inner is bounded by oil;

FIG. 21 is a graph of particle displacement on the inner surface of asubstrate along its length for four frequencies: 1 MHz, 0.85 MHz, 0.7MHz, and 0.55 MHz;

FIG. 22 is a graph of maximum displacement along the inner wall of asubstrate having two adjacent transmit wedges;

FIGS. 23(a)-23(b) depict energy transmission using a finite elementmodel. Each channel includes a 4 ft substrate and 80° wedges, with eachmodel being split into two plots in order to fit on the page.Displacement is plotted. FIG. 23(a) is high contrast (displacement 0.3),and FIG. 23(b) is regular;

FIG. 24 is a picture of an assembled acoustic channel across packer,composed of shear plate transducers on 75° steel wedges epoxied to theoutside of a joint;

FIGS. 25a-25b schematically illustrate shear wave poling in terms ofparticle displacement with respect to a partial cross-section of acasing. FIG. 25(a) (left) shows radial shear displacement(in-wedge-plane poling), and FIG. 25(b) (right) shows tangential sheardisplacement (perpendicular to the wedge plane or out of wedge planepoling);

FIG. 26 is a pair of graphs comparing the efficiency of radial shearpoling (top) and tangential shear poling (bottom) in air and submerged;

FIG. 27 is an alternative schematic diagram of two wedges arranged on asubstrate for transmitting wave energy;

FIG. 28 is a perspective view of a simple acoustic channel with a pairof steel wedges directly mounted to a steel pipe wall;

FIG. 29 is a schematic side view of a pair of transducer/wedgeassemblies on a pipe including layers on the inside and outside of thepipe representing the pipe's surroundings, and a close-up inset;

FIG. 30 is a 2-dimensional beam pattern for longitudinal excitationtransferred from a small steel block into a larger steel block;

FIG. 31 is a 2-dimensional beam pattern for shear excitation transferredfrom a small steel block into a larger steel block.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 is a schematic illustration of a transducers/wedges/pipesubstrate arraignment. This embodiment differs from a most-preferredversion of the invention in that the wedges/blocks 44,54 and thesubstrate 80 are not made of identical materials. Therefore, the angleof the wave is depicted as changing as it passed into and then back outof the substrate 80. Nevertheless the FIG. 1 illustration is helpful tounderstand the different elements of acoustic wedge transmissionsystems. In particular, each transducer typically includes a generallyplanar face 47,57. Each transition wedge preferably has at least oneslanted edge 46,56. The angles of the planar faces 47,57 of thetransducer(s) and of the slanted edge(s) 46,56 of theblocks/wedges/transition wedges 44,54 affect the function of theacoustic channels.

FIG. 27 is a simplified schematic illustration of atransducers/wedges/pipe substrate arraignment of the present inventionwherein the transducer faces 47,57 and slanted wedge faces 46,56 are ata high angle with respect to the substrate 60 below, which may be asteel pipe.

FIG. 28 shows a pair of small triangular steel prisms or wedges joinedto a steel pipe wall and aligned with the axis of the pipe. Alongitudinal or shear piezoelectric transducer is attached to the smallface of each wedge, as shown in the related embodiments in FIGS. 27 and29.

While wedges and transducers are depicted on the outside of pipes in theabove-mentioned figures, embodiments where both transducers and wedgesare on the inside of a pipe, or where one arrangement is on the insideand the other is on the outside, are also within the scope of thisinvention.

Acoustical Channel Simulations

The embodiment of FIG. 29 and related embodiments were tested insimulations. Tests using physical transducer assemblies were alsoconducted, as discussed further below. The height, h, of the inclinedface of the wedge is 10 mm and the launch angle, Θ, varies between zeroand 85 degrees. The “transmitter” transducer 41 is excited by asinusoidal voltage producing a mechanical wave which then travelsthrough the wedge 44 and into the pipe 60 wall. A portion of the energyof that wave will be received by the “receiver” transducer 51 attachedto a reversely oriented second identical steel wedge, such that thecontinuous wave may be received and the acoustic energy harvested. Thereceiver transducer is terminated by a 50Ω load. The substrate pipe hasa wall thickness of 17.78 mm. The simulated channels are bounded invarious simulations by cement, engine oil, air and/or water. Thetransducers are in direct, slipless contact with the wedges so that thewedges and the pipe are effectively a single piece of steel, perfectlyjoined with no discernible interface. If the wedges were attached to thepipe via an adhesive layer or coupling gel rather than welding,reflections at that interface would change the wave field produced.Thus, seamless and like-to-like wedge-substrate couplings are preferred.

Due to the physical size of the channel, with wall thickness of 17.78mm, outer nominal diameter of approximately 0.25 m, and length of up to5 m or more, a true 3-dimensional finite element model would be verycomputationally intensive for wave frequencies on the order of 1 MHz.This makes the model effectively impossible to evaluate with currentcomputers. As such, a 2-dimensional approximation of the FIG. 29 channelwas employed.

The 2-dimensional model effectively treated the pipe as an infinitelywide plate (plane strain). The same is also true for both thetransducers and wedges (infinitely wide plate and triangular prism,respectively). This model approximates the cross-section of the pipe ifthe wedges and transducers stretched completely around the circumferenceof the pipe, although it omits scaling effects of the particledisplacement, stresses, etc., due to the radial distance from the pipe'saxis. The 2-dimensional approximation cannot model motion out-of-plane(circumferential direction) movement.

The complex geometry of acoustic channels have been modeled using thefinite element method, modeling the continuous wave response of thechannel. Finite element simulations can be performed using themulti-physics/FEA software COMSOL. Both longitudinal and in-planeshear-poled transducers have been modeled using finite elements. Finiteelement methods (“FEM”) are useful in simulating transducer/wedgetransmission systems. The finite element method is a numerical techniquefor finding approximate solutions to boundary value problems for partialdifferential equations. It subdivides a problem domain into simplerparts, called finite elements, and uses variational methods from thecalculus of variations to estimate boundary movements and interactionsby minimizing an associated error function. Analogous to the idea thatconnecting many tiny straight lines can approximate a larger circle, FEMencompasses methods for connecting many simple element equations overmany small subdomains or “finite elements” to approximate a more complexequation over a larger domain. In some simulations,Acoustic-Piezoelectric Interaction, Frequency Domain and Acoustic-SolidInteraction, and Frequency Domain modules were used. This modelingtechnique was used to characterize a communication channel throughnormal layers.

In frequency domain finite element simulations (see FIG. 29), there arepreferably at least 5 to 10 elements per wavelength to achieve accurateresults. This is necessary as the model must be able to resolve theacoustic wave appropriately. This study focused on the 0.1 MHz to 1 MHzrange, so elements were constrained to be no larger than 0.4 mm indimension in the wedges and pipe. This corresponds to about one eighththe wavelength of a 1 MHz shear wave, or one sixteenth that of alongitudinal wave. The meshes of the surrounding cement, engine oil andair regions of the models were made finer in proportion to their lowersound speeds (corresponding to shorter wavelengths at a givenfrequency). In the solid materials, the wavelength of a shear wavelimits mesh size because shear waves travel more slowly thanlongitudinal waves. Shear wave speed can usually be approximated as nearhalf the longitudinal wave speed.

Both longitudinal and shear-poled transducers with 1 MHz nominalresonant frequencies were modeled using COMSOL. Using a wedge launchangle of 70 degrees, the transducers behave near ideally at lowerfrequencies (pure longitudinal/shear deformation) as shown in FIGS. 11aand 11b . At higher frequencies, a more complex behavior emerges; seeFIGS. 11c and 11d . This behavioral change at higher frequencies is dueto various additional vibratory modes being excited in addition to thenearly pure shear/longitudinal mode.

FIG. 30 shows a 2-dimensional beam pattern for longitudinal excitationon the end of a 25.4 mm×127 mm steel block attached to a steel blockvibrating at 1 MHz. FIG. 31 shows a two-dimensional beam pattern fortransverse in-plane shear displacement excitation of a 25.4 mm×127 mmsteel block attached to a steel block vibrating at 1 MHz. Thesesimulations are meant to approximate potential diffraction patternsproduced by a similar width wedge transmitting into a large medium.While there is some beam spread in the distances simulated, most of thebeam energy is seen to remain focused within a narrow region.Unfortunately, simulations at large distances, or within a 3-dimensionaldomain are size-prohibitive and therefore, the resulting beam spread atthese distances is difficult or impossible to obtain. Depending on thespecific application, a wide, smoothly distributed diffraction patternmay be a good or bad thing. If the wedge pair can be placed withprecision, a narrow pattern ensures higher energy flux at the receiver.If the final alignment of the wedges is uncertain, a narrow patterncould miss the receiver completely while a wide pattern would give abetter chance of energy reception. Over long distances, perfectalignment is less likely to be achieved. Therefore, transmissionarrangements over longer distances where shear waves of sufficientstrength to be detected at the opposite wedge and transducer, accountingfor beam spread and distance, are contemplated.

Tangential (transversely polarized) shear simulations have beenperformed using the prescribed displacement boundary condition on thetransmitting wedge surface. An example plot is given in FIG. 12. FIG. 12is a finite element analysis (FEA) model for tangential shear waves.Displacement in meters is plotted. 75° steel wedges are used on a 12inch steel plate with oil on the inside (top) and cement on the outside(bottom). Freq(1)=1 MHz, Surface: Total displacement (m).

Tangential shear waves have an out-of-plane component which necessitates3-dimensional models, as shown in FIG. 13. Note that in FIG. 13 much ofthe vibration is towards and away from the perspective of the viewer,into and out of the plane of the page. FIG. 13 is an isometric view of atangential (transversely polarized) shear simulation showing theout-of-plane displacement (75° steel wedges, 1 MHz, 12-inch steel plate,oil on the inside (top), cement on the outside (bottom)).

Typically the receiving wedge on the right will receive the shear wavestransmitted from the launch surface on the left. Note that the identityof the shear waves is maintained when leaving the wedge and entering thesteel substrate. Preferred embodiments also include arrangements wherepower transfer efficiency is at least 0.35%, at least 0.5%, at least0.7%, at least 0.8%, or at least 0.83%. Said power transferefficiencies, in some embodiments, refer to power transfer efficienciesat 4 feet and/or using steel substrates and wedges, or substrates andwedges made of the same metal or metal alloy. Power transfer efficiencymay be affected by the distance being traversed, among other factors.

Piezoelectric transducer arrangements and channels can be modeled usingcomputers. Both transmitting and receiving transducers may berepresented within the models, the transducers being separated by agiven distance. The geometry produced in one such model may be seen inFIG. 15. The excitation voltage applied to the transmitter, or“pitcher”, is specified prior to the execution of the simulation and thevoltage across the “catcher” is extracted directly from the simulationresults, with both values being used to calculate the transmissionefficiency. An example set of results from the described model are givenin FIG. 16, where longitudinal transducers are affixed to 70 degreesteel wedges with the transmit and receive transducer-wedge assembliesbeing placed approximately 16 inches apart on the representativejoint/substrate. Thin, absorptive layers of oil (inside/upper) andcement (outside/lower) are modeled at the boundary of the joint, and atthe axial ends of the representative joint. Non-reflecting boundaryconditions were added to allow for energy to continue propagating awayfrom the system.

FIG. 15 is a simulation with both pitcher and catcher transducers, usinga 1 MHz longitudinal wave. Displacement raised to the fifth root ⅕ isplotted. The exponent serves to increase the contrast of the plot.

Prescribed Displacement Simulations

A second method for simulating transducer/wedge transmission systems(e.g. using finite element code) which avoids the complexity ofsimulating transducers has also been developed. Instead of simulating atransducer per se, a “prescribed displacement” boundary condition isapplied to the face of the simulated wedge. This prescribeddisplacement, or “PD,” boundary condition simply displaces the positionof the simulated transducer-bearing wedge face periodically in the way atransducer would be expected to. The idea is to apply an estimated waveforce to the simulated wedge face without explicitly simulating themovement of the transducer which, in real-world practice, would supplythe wave force to the wedge face. Different transducer polarizationtypes (longitudinal, shear, etc), shapes, and frequencies can beapproximated for different simulations. If the axis of deflection is ina direction tangent to the face, shear waves are simulated. If the axisis perpendicular, longitudinal waves are simulated. This method hasseveral advantages over modeling the transducer itself. Prescribeddisplacement is easier to implement because the model has no electric orpiezoelectric aspects to simulate. This makes prescribed displacementless expensive computationally, allowing for larger and/or fastersimulations of wave transmission arrangements vs. systems wheretransducers are explicitly simulated.

FIGS. 17(a)-18(b) compare prescribed displacement input (FIGS. 17(a) and18(a)) and simulated transducer input (FIGS. 17(b) and 18(b))simulations. FIGS. 17(a)-17(b) compare magnitude of displacement plottedfor longitudinal input excitation. Axes have units of cm. FIG. 17(a) isa prescribed displacement input, while FIG. 17(b) is a transducer inputfor comparison. For both the freq(1)=1 MHz, and surface displacement isin cm. FIGS. 18(a)-18(b) compare magnitude of displacement plotted forshear input excitation. Axes have units of cm. FIG. 18(a) is aprescribed displacement input, while 18(b) is a transducer input forcomparison. For both freq(1)=1 MHz, and surface displacement is in cm.

The actual effect of a transducer on a wedge face may be significantlydifferent from what a full-face prescribed displacement simulation onthat face (i.e., where displacement is same regardless of location onface) can produce. A series of tests aimed at determining the accuracyof the prescribed displacement (PD) approximation were performed. Asdemonstrated in FIG. 17(a) through FIG. 18(b), the PD approximation was,as expected, found to not have high accuracy in the near field; i.e. inclose proximity to the source. See the far left areas of FIG. 17(a)through FIG. 18(b). However, beyond approximately 10 cm, thedisplacement fields produced with a transducer and with the PDapproximation are nearly identical. This observation holds for bothlongitudinal excitation (FIGS. 17(a)-(b)) and shear excitation (FIGS.18(a)-(b)). Since most such systems are intended to transmit energy onscales larger than 10 cm, the PD method is a very useful tool despitenot perfectly replicating the near field behavior of a piezoelectrictransducer.

Wave Frequencies and Transmission Angles

A frequency sweep was performed on a 4 foot beam for three wedge angles(70, 75, and 80 degrees) and across several frequencies. FIG. 14 is agraph of power transfer efficiency as a function of frequency in thatsweep, with wedge angles 70°, 75°, and 80° for transversely polarizedshear waves. The angles refer to the angle of a flat face 47,57 of thetransducer and of the slanted wedge face 46,56 which the transducer isfixed to, with respect to the substrate surface the bottom of the wedgeis fixed to. See FIGS. 1 and 27, and also compare with FIGS. 11(a)-13,15, 17(a)-18(b) and 23(a)-24.

The sweep results (Table 1) suggest that an 80 degree wedge will yieldthe highest power transfer efficiency. Table 1 shows the most efficientfrequencies found for various wedge angles. Subsequent experimentationhas shown that angles of approximately 65, 70, and 75 degrees also workwell. Therefore, embodiments of this invention include arrangements andmethods where transmitting and/or receiving slanted wedge faces, andtheir corresponding transducer faces, each have the following angles (indegrees) with respect to the substrate 60 surface: 65, 70, 75, 80,60-89, 60-85, 60-80, 60-75, 65-89, 65-85, 65-80, 65-75, 68-85, 68-75,68-72, 68-80, 70-80, 70-85, 70-87, 70-89, 75-89, 75-87, 75-85, 75-82,75-80, 77-83, 77-85, 77-87, 78-82, 78-85, 79-81, 80-83, 80-85, and/or80-89. Our results also suggest that frequencies of about 0.3-1.0 MHzare desirable, depending somewhat on the angle selected. Therefore,embodiments of this invention include the preferred wedge angles above,each angle contemplated in combination with each of the followingpreferred frequencies, in MHz: 0.6, 0.8, 1.0, at least 0.1. 0.3, 0.4, atleast 0.6, at least 0.7, at least 0.8, at least 0.9, 0.1-1.0, 0.1-1.5,0.1-2.0, 0.3-1.0, 0.3-1.5, 0.3-2.0, 0.5-2.0, 0.5-1.5, 0.5-1.2, 0.6-1.0,0.6-1.5, 0.6-2.0, 0.7-2.0, 0.7-1.5, 0.7-1.3, 0.7-1.2, 0.7-1.0, 0.8-1.5,0.8-1.3, 0.8-1.2, 0.8-1.0, 0.9-1.2, 0.9-1.1, and 0.9-1.0. Alternativearrangements include a wedge angle in degrees of 75, 74-76, 73-77 or72-78, each in combination with a transmission frequency in MHz of 9.0,8.9-9.1, 8.7-9.3, 8.5-9.5, 8.0-10.0.

TABLE 1 Dead Zones-Wedge Spacing and Excitation Frequency Wedge anglePeak frequency Efficiency 70° 0.80 MHz 0.18% 75° 0.90 MHz 0.35% 80° 1.00MHz 0.83%

FIG. 16 shows voltage at a harvesting transducer, plotted over oneperiod for five different positions of the catching wedge, correspondingto five different spacings between the pitcher and catcher: 86 cm, 88cm, 90 cm, 92 cm, and 94 cm.

As can been seen from FIG. 16, depending on the location of the wedgesalong the substrate joint, the arrangements may experience “dead zones,”where the overall energy imparted on the surface of the substrate and,therefore, transmitted into the receiving wedge is significantly reducedas compared to more optimal placements and spacings. Dead zones mayappear at intervals along the substrate, and their locations may varybased on parameters of the transmission system such as transmissionfrequency, angle, and channel material. See FIG. 21 and below.

A series of five simulations were completed where the spacing betweenthe wedges was moved between 86 and 94 cm, in 2 cm increments (34 and 37inches, 0.8 inch increments), in order to show this dead zone effect.The voltage seen at the receiver for each case is given in FIG. 16. Thisplot shows that the placement of the wedge at an optimal location willhave a significant impact on the receiver voltage, with the maximumreceived voltage amplitude produced by these simulations being slightlylarger than 30 mV, with a minimum received voltage amplitude beingsubstantially lower at approximately 22 mV. It should be noted that forthis model and set of simulations, the transmitter was excited with 100V, the receiver was terminated with a 50Ω load, the wedges had an angleof 70 degrees, and the thickness of the casing is 0.7 in.

Therefore, one aspect of the present invention is determining optimalplacement and spacing of wedges for a given arrangement to maximizetransmission efficiency and, as a corollary, to avoid placing areceiving wedge in a dead zone on the substrate. This method can includeselecting approximate locations for send and receive transducer wedgesbased on the desired function and setup, and then testing the efficiencyof energy transfer between the wedges as one of the wedges is movedsmall steps closer or further from the other wedge to determine anoptimum exact location in the desired general area. Either the send orthe receive wedge may be stepped, depending on circumstances. The wedgebeing stepped may be stepped by, for example, 0.25 cm, 0.5 cm, 1 cm, 2cm, or 3 cm intervals through the available mounting area. Preferablythe optimization process is conducted using the wedge angle, transmitfrequency, substrate material, and other parameters that the arrangementwill operate under. A position of maximum efficiency in the desired areais identified, and a transducer and wedge are then fixed or otherwiseprovided at that position. A preferred embodiment of the presentinvention includes using preferred materials, frequencies, shear waves,and launch angles as discussed elsewhere in combination with using astepping process to optimize wedge placement and avoid dead zones,preferably for each new installation or type of installation.

As mentioned, dead zone locations and sizes depend on a variety offactors including the frequency of excitation and the input angle. InFIG. 21, the total displacement of the inner surface of the joint isgiven along its length for four different excitation frequencies (1,0.85, 0.7 and 0.55 MHz). It was determined that as the input frequencyis reduced, the troughs become less apparent and so dead zones are lessof a factor at larger distances from the transmitting wedge. However asfrequency is reduced, the magnitude of the displacement is also reduced,especially further away from the transmitting wedge, and so less energyis available to detect and use as a power source at a receiving wedge.The unlabeled vertical scale is relative in FIG. 21 as displacements aredependent on the magnitude of the prescribed displacement, an arbitraryquantity. Higher frequency waves “beam” more effectively while lowerfrequencies spread out more quickly due to diffraction. While notwishing to be bound by theory, this is thought to explain thecorrelations between amplitude, peakiness, and frequency.

An extended joint length simulation was performed. For this evaluation,the model was constructed with an 80 degree transmit wedge and a 4 ftlength of joint as the substrate. The wedges were excited in the inplane (radial) shear mode. The results of this evaluation are given inFIGS. 23(a)-23(b). FIGS. 23(a)-23(b) depict extended length evaluationsof finite element model. Each is a 4 ft length with 80° wedges, witheach beam being split into two plots in order to fit on the page.Displacement is plotted. FIG. 23(a) is high contrast (displacement 0.3),and FIG. 23(b) is regular. These plots show fairly regular and periodicbehavior of the displacement throughout the length of the joints.

Axially longer receiving wedges have a greater probability of contactinga strong vibration receiving areas of the substrate, as opposed to adead zone. Receiving wedges having an axial length of about 2.5-3 inchesare useful. Wedges with axial lengths of about 2-3 inches, 2-3.5 inches,1.5-3.5 inches, 1-4 inches, and 2-4 inches are also contemplated,without limitation.

Channels with Multiple Send or Receive Wedges

In an effort to reduce the likelihood of placing the receiving wedge ona dead zone, systems with two transmitting wedges (one immediately afterthe other axially) were modeled. The resulting inner surfacedisplacement is shown in FIG. 22, using an input frequency of 1 MHz.Comparing this plot with the results given in FIG. 21 shows less clearlydefined dead zone behavior, with the displacement magnitude being lessvariable with the distance from the sources. Transmission efficiency wasnot diminished by the use of two wedges. Embodiments using two, three,or more transmitting wedges in series are therefore very promising andare part of this invention, particularly for embodiments wheretransmission conditions/parameters are likely to vary over time, and/orwhere it is not possible or practical to optimize the placement of thewedges, such as by a stepping process. The send arrangement and/or thereceive arrangement may include multiple wedges, each holding atransducer.

Efficiency Effect of Incident Angles and Boundary Conditions

Using the PD approximation, a series of simulations were completed inorder to determine how the incident angle of the transmitted waveaffects the effective attenuation rate. These simulations were performedwith just a transmitter wedge (steel) attached to a joint plate, withthe receiver wedge omitted. Energy flux in the plate was recorded at adistance of 8 in from the transmitting wedge for input angles from 0degrees (transmission direction perpendicular to the joint wall, maximumsteepness, transducer facing downwards) to 80 degrees (transmissiondirection nearly parallel to the joint wall, transducer face nearlyvertical, similar to FIG. 27).

The evaluations were performed with the plate substrate in the air andalso in water. The results are presented in FIG. 19. The “efficiency”levels in the chart refers to output energy flux, normalized by theenergy flux at the input face. I.e., the fraction of the energy at thetransmit wedge which is received at the plate face where, normally, areceive wedge would be. In FIG. 19, the upper two series of data points(X and O) are both dry conditions, and the lower two (also X and O) areboth submerged.

As shown, when the joint is in air and not submerged, shear wavetransmission (normally created by shear transducer excitation) is moreefficient than longitudinal transmission at most incident angles. Seethe upper two series of X and O. When the substrate is submerged,however, the superiority of shear versus longitudinal transmissionvaries depending on the incident angle. Specifically, at steeper inputangles less than 40 degrees, longitudinal excitation is more effective,while shear mode transmission provides greater efficiency at mostshallower (i.e. greater) incident angles. Therefore, aspects of thisinvention include using input angles of at least 50, at least 60, atleast 70, at least 80, 50-89, 60-89, 60-80, 60-85, 70-89, 70-85, or70-80 with shear wave transmission when the transmission channel is in adry environment. Other aspects include using shear vibrations and aninput angle in degrees of 25, 20-30, 15-35, 15-30, 10-25, 10-30, or10-35 when the channel is in a submerged environment, especially withliquid on all sides. Another aspect is using longitudinal vibrations andan input angle in degrees of 50-70, 45-70, 50-65, or 45-70.

A second, especially relevant set of transmission simulations included avirtual receiving wedge and boundary conditions similar to those in anoil well. Energy transmission between a transmitting wedge and a sectionof the inner surface of the pipe, effectively a virtual receiving wedge.These simulations used boundary conditions of cement on the outside andengine oil on the inside. The section of the pipes surface that wasmonitored for energy flux was 8 cm long and started 32.6 cm from thetransducer. The results of these simulations are given in FIG. 20. Underthese “real world” conditions, arrangements using a shear waves at ashallow input angle (70 to nearly 90 degrees) were clearly superior toarrangements using longitudinal waves and arrangements using steeper(i.e. lower) input angles. Therefore, most preferred embodiments of thisinvention include embodiments where the channel substrate has a solidbarrier on one side and liquid on the other side, for example, a pipefor carrying oil, water, or other liquids which is encased in concreteand/or underground. Preferably shear wave transmission is used in sucharrangements, and most preferably tangential shear wave transmission.Preferably high input angles are used. Specifically, in degrees, atleast 65, 70, 75, 80, or 85 degrees, or within the following ranges:60-70, 70-89, 70-85, 75-89, 75-85, 80-89, 80-87, 80-85, 83-89, 83-87,83-85, 85-89, or 85-87.

Tangential Shear Poling is Superior to Radial Shear Poling in SubmergedConditions

In addition to the computer simulations discussed above, physicaltesting was also performed with transducer/wedge/substrate acousticalarrangements. In total, seven wedge channels were assembled and testedon a joint substrate, with the packer. For each channel, the packer waswithin the acoustic propagation path and a shear plate transducer wasused. FIG. 24 is a picture of an assembled acoustic channel acrosspacker, composed of shear plate transducers on 75° steel wedges epoxiedto the outside of a joint. The first transducers assembled onto a jointwere shear plate piezoelectric mounted on 75° steel wedges, which werespaced 4 feet apart across the joint with packer located inside thesection of joint that lies between the wedges. The steel wedges in thischannel had a flat interface machined onto them, meaning that the bottomsurface did not match the curvature of the joint and, therefore, thethickness of the epoxy layer was variable with respect to thecircumferential location. Note that more preferred embodiments do notuse epoxy or other adhesives. Rather, wedges and substrates are made ofthe same material, and which have no other material or empty spacesbetween them. For example, a direct steel-steel bond, or wedges pressedfirmly against the substrate, such as by a clamp, wrap, tape, cable,elastic member, or other external compression means.

An important aspect of the assembled channels (wedge-pipe wall-wedge) isthe direction of poling of the shear transducers, which refers to theparticle displacement direction of the generated acoustic wave withregard to the plane of the acoustic wedge). FIGS. 25(a)-25(b)schematically illustrate radial vs. tangential shear wave poling withrespect to a partial cross-section of a pipe casing. 25(a) (left) showsradial shear displacement (in-wedge-plane poling), and 25(b) (right)shows tangential shear displacement (perpendicular to the wedge plane orout of wedge plane poling). The first two channels assembled were testedin part to determine the effect of the different polings on channelefficiency. It was shown in the tests that tangential shear poling issuperior to radial shear poling in a submerged environment.

FIG. 26 is a pair of graphs comparing the efficiency of radial shearpoling (top) and tangential shear poling (bottom) in air and submerged.For each of the following channel characterizations, both the in-air(black) and submerged (gray) results are given on the same plot.Referring to FIG. 26, in air both the radial and tangential channels arecapable of similar power transfer efficiencies. However, when placed ina tank with water, the radially poled channel's capacity falls off,while the tangential channel maintains a similar, or at least adequate,efficiency across most frequencies. Though not wishing to be bound bytheory, this difference is understood to be due to greater and lesserdegrees of interaction with surrounding water, which irretrievablyremoves transmission energy from the channel. Compare FIGS. 25(a) and25(b), imagining liquid on at least one side of the substrate. When thevibrations in the metal wedges and substrate are radially poled(in-plane polling—FIG. 25(a)), interaction with the water at thesurfaces creates longitudinal waves in the water, meaning thatvibrational energy leaves the channel. When the displacement istangential to the surface of the pipe, however, (FIG. 25(b)) there isfar less water/channel surface interaction. There is therefore far lessenergy loss to the surrounding water with tangential shear poling, andless energy is thereby lost in a submerged system. As a result of thesefindings, certain most preferred embodiments of this invention utilizetangential shear polling and transversely polarized shear transducers totransmit energy, particularly when at least part of the channel is incontact with a liquid such as water or oil. When the channel surfacescontact air, in contrast to liquid, the interactions with surroundingparticles absorb far less energy, so the difference between radial andtangential polling is much less pronounced. Consider, analogously, howit requires more effort to push your hand a given distance through waterthan through air.

Horizontal and circumferential poling are subtypes of tangential shearpoling, which are specific to planar and tubular substrates,respectively. Horizontal and circumferential poling are thereforecontemplated and interchangeable where “tangential” shear waves andtangential poling are discussed in this document, where appropriate.

CONCLUSION

The present invention includes both methods and apparatus based on theabove disclosures. The present invention includes methods of assembling,optimizing, and testing transducer driven transmission systems. It alsoincludes methods of testing and simulating transducers and acoustictransmission arrangements.

Nothing in this disclosure shall be construed as a representation oradmission regarding what is or is not prior art absent a specificstatement to that effect. The inclusion of material in the backgroundsection or any other section, for example, is not to be construed as arepresentation regarding what is or is not prior art.

The elements, systems, and methods disclosed herein are contemplated anddisclosed in all reasonable combinations and sub-combinations. It shouldbe understood that various preferred elements disclosed herein can beused both separately and together. While a specific embodiment of theinvention has been shown and described in detail to illustrate theapplication of the principles of the invention, it will be understoodthat the invention may be embodied otherwise without departing from suchprinciples.

What is claimed is:
 1. A method of transmitting at least one of powerand signals along a steel oil pipe using tangential shear waves, themethod comprising: providing a transmitting arrangement and a receivingarrangement spaced apart on a steel oil pipe; wherein the oil pipe hasconcrete on at least a portion of an outer surface, and wherein, in anoperative state, oil is in contact with an inner surface of the oilpipe; wherein each transmitting arrangement comprises a steeltransmitting wedge and a transmitting transducer coupled to thetransmitting wedge, and wherein each receiving arrangement comprises asteel receiving wedge and a receiving transducer coupled to thereceiving wedge; wherein the transmitting transducer comprises a flattransmitting face for emitting tangential shear waves, the transmittingface of the transmitting transducer being coupled to an angled face ofthe transmitting wedge; wherein the transmitting face of thetransmitting transducer and the angled face of the transmitting wedgeare both normal to an angle Θ with respect to the surface of the oilpipe which the transmitting wedge is coupled to; wherein the angle Θ isan angle of at least 65 degrees and not more than 85 degrees; the methodfurther comprising the transmit transducer producing tangential shearwaves at angle Θ, with said shear waves propagating through thetransmitting wedge and into the oil pipe, through the oil pipe, and theninto the receiving wedge, with said tangential shear waves beingreceived by the receiving transducer; wherein said tangential shearwaves substantially remain tangential shear waves as they propagatethrough the transmit wedge, the oil pipe, and the receiving wedge; andthe receiving transducer converting at least a portion of an energycontent of said tangential shear waves into electrical energy.
 2. Themethod of claim 1, wherein the angle .theta. is an angle of at least 70degrees and not more than 83 degrees.
 3. A method of transmitting atleast one of power and signals along a substrate using shear waves, themethod comprising: providing a transmitting arrangement and a receivingarrangement spaced apart on a substrate; wherein each transmittingarrangement comprises a transmitting wedge and a transmitting transducercoupled to the transmitting wedge, and wherein each receivingarrangement comprises a receiving wedge and a receiving transducercoupled to the receiving wedge; wherein the transmitting transducercomprises a flat transmitting face for emitting shear waves, thetransmitting face of the transmitting transducer being coupled to anangled face of the transmitting wedge; wherein the transmitting face ofthe transmitting transducer is normal to an angle .theta. with respectto the surface of the steel substrate which the transmitting wedge iscoupled to; wherein the angle Θ is an angle of at least 65 degrees andnot more than 89 degrees; the method further comprising the transmittransducer producing shear waves at angle Θ, with said shear wavespropagating through the transmitting wedge and into the substrate,through the substrate, and then into the receiving wedge, with saidshear waves being received by the receiving transducer; wherein saidshear waves substantially remain shear waves as they pass through thetransmit wedge, the substrate, and the receiving wedge; and thereceiving transducer converting at least a portion of an energy contentof said shear waves into electrical energy.
 4. The method of claim 3,wherein the arrangement comprises a plurality of transmittingarrangements, with said transmitting arrangements positioned in seriesalong an axial length of the pipe; and wherein said transmittingarrangements all produce shear waves.
 5. The method of claim 3, whereinthe substrate, the transmitting wedge, and the receiving wedge allcomprise steel.
 6. The method of claim 3, wherein the substrate, thetransmitting wedge, and the receiving wedge all comprise steel, andwherein each transmitting wedge and each receiving wedge is directlybound to a surface of the substrate by a direct steel-steel bond.
 7. Themethod of claim 3, wherein the substrate, the transmitting wedge, andthe receiving wedge are all made of the same material.
 8. The method ofclaim 3, wherein the shear waves are tangential shear waves.
 9. Themethod of claim 3, wherein the angle .theta. is an angle of at least 70degrees and not more than 85 degrees.
 10. The method of claim 3, whereinthe shear waves are tangential shear waves; and wherein the angle.theta. is an angle of at least 70 degrees and not more than 85 degrees.11. The method of claim 3, wherein the substrate is a metal pipe, andwherein the transmitting wedge and the receiving wedge are both made outof a same metal as the metal pipe.
 12. The method of claim 3, whereinthe substrate is a pipe; wherein the transmitting arrangement is aboveground level; and wherein the receiving arrangement is below groundlevel.
 13. The method of claim 3, wherein the substrate is an oil pipe,wherein the oil pipe has concrete on at least a portion of an outersurface, and wherein, in an operative state, oil is in contact with aninner surface of the oil pipe; and wherein the shear waves aretangential shear waves.
 14. The method of claim 3, wherein the substrateis a steel oil pipe, wherein the oil pipe has concrete on at least aportion of an outer surface, and wherein, in an operative state, oil isin contact with an inner surface of the oil pipe; wherein thetransmitting wedge and the receiving wedge are both made out of steel;and wherein the shear waves are tangential shear waves.
 15. The methodof claim 3, wherein transmissions are also sent in a reverse direction,from the receiving acoustic wedge to the transmitting acoustic wedge,using shear waves produced by the receiving transducer.
 16. Anarrangement for transmitting at least one of power and signals along apipe using shear waves, the arrangement comprising: a transmittingarrangement and a receiving arrangement spaced apart on the pipe;wherein each transmitting arrangement comprises a transmitting wedge anda transmitting transducer coupled to the transmitting wedge, and whereineach receiving arrangement comprises a receiving wedge and a receivingtransducer coupled to the receiving wedge; wherein the transmittingtransducer is a shear wave transducer, and is positioned on thetransmitting wedge so that, in operation, the transmitting transducerwill send shear wave vibrations into the transmitting wedge; wherein thetransmitting transducer comprises a flat transmitting face for emittingshear waves, the transmitting face of the transmitting transducer beingcoupled to an angled face of the transmitting wedge; wherein thetransmitting face of the transmitting transducer is normal to an angle Θwith respect to the surface of the pipe which the transmitting wedge iscoupled to; wherein the angle Θ is an angle of at least 65 degrees andnot more than 89 degrees; and wherein the transmitting wedge, the pipe,and the receiving wedge collectively form a continuous acoustic channel,the channel being capable of carrying shear wave vibrations between thetransmitting transducer and the receiving transducer.
 17. Thearrangement of claim 16, wherein the pipe is an oil pipe; wherein theoil pipe has concrete on at least a portion of an outer surface, andwherein, in an operative state, oil is in contact with an inner surfaceof the oil pipe.
 18. The arrangement of claim 16, wherein the pipe, thetransmitting wedge, and the receiving wedge all comprise steel; andwherein each transmitting wedge and each receiving wedge are directlybound to a surface of the pipe by a direct steel-steel bond.
 19. Thearrangement of claim 16, wherein the arrangement comprises at least twotransmitting arrangements, with said transmitting arrangementspositioned adjacent to each other and in series along an axial length ofthe pipe.
 20. The arrangement of claim 16, wherein the angle .theta. isan angle of at least 70 degrees and not more than 85 degrees.